The search for biological control methods has taken increasing importance in recent years. Substitutes are needed for established methods involving the use of esoteric chemicals with troublesome lingering residues as described in Rachael Carson's Silent Spring. Another goal of biological control is to provide economically feasible solutions to certain problems such as the damage caused by Fomes annosus, disease fungus attacking many forest tree species, or the damage caused by Ceratocystis ulmi to elm trees and by Botrytis to grapes.
In the investigation of biological control methods, many attempts have been made at manipulating the microbial population of the rhizosphere and other components of the external environment of plants, particularly in the soil. Most of these attempts failed, often because of the extreme diversity of chemical and biological factors present in such a system, resulting in great "buffer" capacity. A few instances of noticeable successes were obtained, as in the control of Phymatotrichum root rot of cottom, Ophiobolus root rot of wheat, Streptomyces scab of potato, Fusarium root rot of bean, Sclerotium stem rot of peanut, and a Fomes root rot of the rubber tree in Malaya.
The present inventor has discovered a new approach to biological control, namely the utilization of microbial immunizing commensals. The concept was reduced to practice under actual field conditions demonstrating its effectiveness in terms of the traditional cirteria for cause-to-effect relationships in microbiology and related fields, the postulates of Koch.
Immunizing commensals are microorganisms which can exist in the internal environment in contrast with the external environment or surroundings, soil for example, of higher plants and animals or other substrates. They grow internally of the plant or other host to be protected without causing damage to it, and at the same time establish a population of an immunizing commensal which controls or eliminates undesired pathogens. Occurrence of these microorganisms provides protection to their host against certain harmful microorganisms.
This concept and numerous specific techniques for carrying it out are fully described in the present inventor's co-pending U.S. patent application Ser. No. 883,272, which is herein incorporated by reference. Prior patents issued or applied for in this and related areas include U.S. Pat. Nos. 3,255,905 and 3,424,655, to Jacques L. Ricard, the inventor in the instant application; U.S. Patent Application "Wood Protection Process and Antibiotic" by Jacques L. Ricard and Walter B. Bollen, filed in January, 1967; U.S. Patent Application "Immunizing Commensals Utilization Method," filed by the same Jacques L. Ricard in June, 1967; French patent application Ser. No. 119,895 for a process of obtaining microbial commensals and for their utilization to combat microbes, insects and other organisms harmful to plants, animals and man, and products of the process; and a U.S. Patent Application for "Extruded Bark Pellet," filed by the same Jacques L. Ricard and Raymond A. Currier on Feb. 10, 1969.